1. Technical Field
The present invention relates to an optical switching device (light valve) used for optical communication, optical operation, an optical storage, an optical printer, a picture display device, etc. and, more particularly, to a picture display device and an optical switching device applicable to a projection apparatus or the like.
2. Background Art
A picture display device such as a projector primarily employs a liquid crystal display device 900 that uses liquid crystal as an optical switching device as shown in FIG. 21 which provides a schematic configuration thereof. The liquid crystal display device 900 formed of a polarizers 901 and 908, glass plates 902 and 903, transparent electrodes 904 and 905, and liquid crystals 906 and 907 provides pixel display by applying a voltage between the transparent electrodes to change the orientations of liquid crystal molecules thereby to rotate polarizing surfaces. Images are presented by using a liquid crystal panel constituted by pixels which are formed of such optical switching devices (liquid crystal cells) and are two-dimensionally arranged, and by adjusting an applied voltage to control the orientations of liquid crystal molecules so as to perform gray-scale representation.
Liquid crystal, however, exhibits poor fast-response characteristic and operates at a response speed of only about a few milliseconds at most. There has been another problem in that the polarizers deteriorate light utilization efficiency of liquid crystal, and an attempt to obtain a higher contrast ratio considerably adds to power consumed. For this reason, as a picture display device that is required to provide still higher picture quality, there have recently been demands for a picture display device capable of providing brighter display with more accurate gray scale representation than a liquid crystal display apparatus.
In recent years, a picture display device has been under study that employs an optical switching device capable of quickly turning light ON/OFF by bringing an optical switching assembly, which is equipped with a light transmitting micro prism capable of extracting light, close to a light guiding member that is capable of transmitting light by means of total reflection so as to extract evanescent light (evanescent wave) and by a minute movement of about one wavelength or less. The picture display device employing such an optical switching assembly is expected to be able to provide brighter picture display with higher contrast since the picture display device is capable of operating at faster speed because of a shorter moving distance and also capable of enhancing light utilization efficiency. However, the picture display device utilizing evanescent light is still in a developing phase, and it has not yet necessarily become able to provide higher efficiency of light utilization and high-quality images with higher contrast.
Accordingly, an object of the present invention is to provide a picture display device capable of enhancing the efficiency of light utilization so as to provide higher quality pictures with higher contrast by optimizing a picture display device employing an optical switching device utilizing evanescent light, particularly by optimizing a path or the like of an incoming light ray applied to a display area provided on a total reflection surface. Another object of the invention is to provide an optical switching device ideally suited for such a picture display device.